Method and apparatus for analyzing water and other solutions



July 8, 1941 w. F. LANGELIER METHOD AND APPARATUS'FOR ANALYZING WATERAND OTHER SOLUTIONS Filed Aug. 28, 1939 FIG.

W/LFRED E/LA/VGELIER INVENTOR.

I HIS ATTORNEY.

Patented July 8, 1941 METHOD AND APPARATUS FOR/ANALYZING WATER AND OTHERSOLUTIONS Wilfred F. Langelier, Berkeley, Calif.

Application August 28, 1939, Serial'No. 292,267

13 Claims.

This invention relates to testing water with respect to soap, the wordwater being intended to include besides natural water also artificialaqueous solutions. analyzing water for its content of certain metals bymeans of soap and to the testing of soap by means of water of knowncontent of certain metals, as Well as to other tests involving areaction between soap and water. By the expression testing water withrespect to soap it is intended to include the determination of theequivalent amounts of soap and water (wherein either the water or thesoap may be the un- More particularly, it relates to V V V quired toform a permanent layer of suds or known, or both the strength of thesoap and the hardness of the water are known and the influence of athird agent is sought) as Well as the determination of Whether a givenmixture of soap and water contains a quantity of soap which is in excessof or less than the equivalent amount. This application is acontinuation in-part of my copending application Serial No. 229,685,filed September 13, 1938.

The invention may be applied to determine the hardness of water, i. e.,to find its content of calcium, magnesium, and other metals whichinfluence the suds-forming characteristics by titration against astandard soap solution, or merely to determine whether the hardness ofthe water is greater or less than a specified quantity. The water may,for example, be natural or softened water, or a solution containing aknown quantity of soil or of a mineral which it is desired to analyzeIor metals, prepared by dissolving the mineral in an acid, neutralizing,and diluting with distilled water.

It may also be used to evaluate soap by titrating it against a Watersolution containing a known amount of dissolved metal such as calcium,i. e., having a known hardness. It may be a liquid soap or a solution ofcomminuted soap dissolved in distilled water or in aqueous ethylalcohol.

Further, the invention is suitable for evaluating anti-foam compositionsmarketed for .preventing the formation of foam or lather, such ascaprylic alcohol, rosin solutions, etc. .In this em 4 bodiment ameasured quantity of the anti-foam agent is placed into the testingreceptacle together with distilled water or with Water of knownhardness, and the resulting mixture is titrated against a standardizedsoap solution, the quantity of soap required to reach the end pointbeing indicative of the foam-preventing power of the agent. I

Other uses of the invention will occur to one reading the presentspecification.

The use of soap to determine the hardness of water is founded upon thefollowing considerations: When soap is mixed with distilled Water andair, a certain small quantity of soap is relather on the surface whenthe Water is quiet.

When, however, the water contains certain metallic ions, particularlycalcium and/or magnesium, the metallio'ions react with the soap and theformation of suds is' prevented until an additional quantity of soap,dependent upon the quantity of such ions in the water, has been added.By subtracting Ifrom the total quantity of soap required in any instanceto produce suds a value known as the lather factor, (which correspondsapproximatelyto the aforesaid small quantity) one obtains a quantity ofsoap, which is proportional to the hardness of the water. This hardnessmay be expressed in terms of the actual metals present, or as parts ofcalcium carbonate per million parts of water.

The methods heretofore proposed'to determine the equivalent quantitiesof soap and water involve observing the lather at the surface. Of thesethe so-called handmethod is the most accurate; it is a static method, i.e., it involves the observation of the suds while the Water isquiescent. As described in Standard Methods for Examination of Water andSewage, published by the American Public Health Association, it involvesmeasuring a 50 ml. (milliliter) sample of the water into a 250 ml. glassstoppered bottle, adding standardized soap solution in portions of 0.2to 0.3 ml., and shaking the bottle by hand vigorously for 15 secondsafter each addition. When suds appear, the bottle is laid on its sidefor five minutes, and the end point is found when the lather on thesurface remains unbroken for 5 minutes. In this test the soap solutionconsists of pure castile soap or sodium or potassium oleate dissolved inethyl alcohol, and it is standardized by titrating it in the 250 ml.bottle as described above against an aqueous solution of calciumchloride having a concentration. equivalent to parts per million ofcalcium carbonate. The soap solution is diluted so as to have a strengthequivalent to about 0.6 to 1.1 mg. (milligrams) of calcium carbonate perml. of soap.

.The necessity for waiting five minutes each time before deciding thatthe end point has been reached, for employing a proper and uniformintensity of shaking, and for the exerciseof a considerable degree ofjudgment as to the appearance of the suds which are incidents of thehand method, arise from the different speeds with which different metalsreact with the soap. Thus, when water contains both calcium andmagnesium the calcium normally reacts with the soap instantaneously,with the result that suds appear when less than the equivalent amount ofsoap has been added, and only the calcium, but not all of the magnesium,has reacted. In this case a ghost end point is reached and the suds arenot permanent but break, usually within five minutes, and sometimespresent to the eye of a skillful operator an appearance different fromthat of the true end point suds. rect intensity of shaking alters theresults, since too slow a motion does not disperse enough air in thewater to produce suds which are permanent, and, on the other hand, doesnot insure that all of the metals come in contact with the soap, tendingto give too early an end point, thus causing to opposing errors. Alsothe results are influenced by the ratio of the metals in the water. Forexample, it was found that when the ratio of magnesium to calcium issmall, such as less than 1 to 4, the magnesium will often react veryslowly or not at all, resulting in the formation of suds which persistover five minutes although magnesium ions are still present, yieldingtoo low a value for the determined hardness; on the other hand, when theratio of magnesium is greater than 1 to 3, an excess of soap is oftenrequired to cause all of the magnesium to react and to form permanentsuds, resulting in too high a value for the determined hardness.

It has also been proposed to employ dynamic methods, wherein the water,air and soap are Also, an incormixed mechanically and the end point isdetermined while the water is in motion, by observing the formation oflather on the surface (Patent 2,112,824) or by permitting the suds tooverflow from the surface onto an indicating or weighing device (Patent1,643,243) These proposed methods, however, do not determine thepermanence of the suds and for this reason give erroneous results when aghost end point is encountered. The limitations as to the maximumoperating speed, as explained below, make it impossible to operate thesedevices at speeds which insure a reaction rate of the magnesium and thelike which is high enough to insure that suds are formed only when thetrue end point has been reached.

A further source of inaccuracy in these dynamic methods is that it isdifficult or impossible to select a speed of mixing which will givereproducible results, in view of the following conflicting requirements:On the one hand, a fairly strong agitation with air is required toinsure contact between the soap and the metals in the water, and todisperse the air sufficiently to produce a froth, it having been foundthat when mechanical devices are operated at relatively low speeds fargreater quantities of soap, often twice the equivalent amount or more,are required to form suds than at higher mixing speeds. On the otherhand, a high degree of agitation is inherently undesirable becauseagitation breaks up the suds on the surface and even prevents suds fromforming by retaining the soap beneath the surface of the water, with theresult that a larger quantity of soap must be added to form arecognizable layer of suds at the surface than would be required if lessagitation or no agitation were used. The error due to these causes isnot, however, constant and no simple correction therefor can be made.

Moreover, in such methods the end point is not sharply defined becausethe movement of the water prevents a building up of the suds, and thesuds appear gradually in patches, the first patches of suds beingvisible long before the end point. It is, therefore, necessary to relyupon judgment 'as to when the end point is reached. Reliance uponmechanical indicators, such as a photo-cell arranged to cause the sudsto interrupt a beam of light or an overflow weir do not increase theprecision because the motion of the water prevents the suds frombuilding up to a reproducible height when the end point is reached.

7 According to the present invention it was found that water can betested with respect to soap, and that the equivalent amounts of soap canbe determined, much more accurately, rapidly, conveniently, and with agreater degree of reproducibility, by agitating the mixture of soap andwater in the presence of dispersed air with a speed sufficient to causethe mixture to become substantially opaque to light when at least theequivalent amount of soap is present, and observing the transparency ofthe agitated or moving mixture, preferably through a fixed observingdepth, to determine whether it has a predetermined opacity. As used inthis specification and claims, the equivalent amount of soap is thetotal quantity of soap required to reach the end point, i. e., itincludes the lather factor, the hardness of the water being determinedby subtracting the lather factor from. the equivalent amount. It wasfound that when soap is gradually added to water which is agitated underthese conditions there is a sharp increase in the opacity of the mixturewhen the equivalent amount of soap has been added, giving a readilyreproducible end point. In this method little or no lather is formed onthe surface of the water when the end point is reached due to the strongagitation employed, practically all of the soap being retained in thebody of the water where it aids the formation of an opaque air-in-waterdispersion. It was further found that such a strong degree of agitationpromotes the reaction of magnesium and similar slow-reacting metals withthe soap, and thereby avoids the false end point and obviates thenecessity of testing suds for permanence. In the usual mode of operationwherein a quantitative evaluation of soap or water is desired, the soapis added to the water progressively until the predetermined degree ofopacity is observed. The method is, however, also applicable tooperations wherein soap and water are mixed in a fixed ratio, theresulting mixture is agitated in the presence of dispersed air, and thewater is observed to determine merely whether or not the saidpredetermined degree of opacity occurs.

As used in the present specification and claims the term lather isintended to denote a dispersed system of globular liquid films enclosingvapors or gases, such as air. The term air-inwater dispersion isintended to denote a dispersed system comprising small bubbles of airdispersed in water, the water being in a mobile form, 1. e., a system inwhich the water forms a continuous phase Which is not in the form of afilm.

This method differs from the hand method in that the end point isdetermined under dynamic conditions, avoiding the need for Waiting tofind out whether the suds are permanent, and makins it possible tocomplete a hardness determination in from one to five minutes, in thatamore uniform intensity of agitation is made possible,

served. It differs from the dynamic methods according to the above citedUnited States patent specifications in that it'permits a strongagitationto cause all of the metals to be intimately mixed with the soap andquickly reacted therewith, and in that it makes it possible to select amixing speed which givesreproducible'results.

It differs further in that at the equivalence-point the formation of alather at the surface of the air-in-water dispersion is entirely or'for.the greater part prevented, and .in that the equivalence or end pointis determined by observing the opacity of the air-in-waterdispersionbeneath the surface instead of the appearance or thickness ofa lather on the surface of the airin-water dispersion.

Toohigh a degree of agitation and too'finea dispersion of agreatquantity of air in the air-t in-water dispersion should, however,be avoided, because it was found that when the speed of the mixingdevice described herein is too great the air-in-water dispersion becomesopaque before the magnesium has completely reacted. This zlj is believedto be caused by anexcessive increase in. the air-water interface areawhich preferentially adsorbs the soap, thereby giving anapparent endpoint before the soap has reacted with all of the metals.

The method is preferably carried out in theapparatus described herein,but the use of other devices performing equivalent-functions ofaeratingthe water, mixing it with soap, and agitating it in an observingzone with a turbulence sufficient to promote the reaction and to retainthe suds in the'water, may also be employed.

In the drawing, Figure 1 is a side elevation of the preferred form ofthe apparatus; Figure 2 is an enlarged front elevation, partly insection;

of the same apparatus; Figure 3 is a sectional view on section line 3--3of Figure 2; and Figure 4 is a sectional view of a modified formemploying a photo-electric cell.

Referring to Figures 1 to 3, l is a base having a recess 2 to collectliquid accidentally spilled, carrying a vertical rod 3. A slidablesleeve 4 on the rod supports electric motor 5 and is secured by a clampscrew 6. The motor is energized by electric wires I, having a switch 8,and controlledby a rheostat 9 having a regulating knob It]. A

water motor or a hand driven gear drive can be used instead of theelectric motor.

The armature shaft of the motor carries a propeller shaft I I carryingthree vanes l2, to impart a downward movement to water. A cylindricaldraft-tube l3 open at the bottom surrounds the propeller shaft andextends slightly below the propeller vanes. It issecured to the motor byset screw l4. Two diametrically opposed observing holes i5-larger thanthe diameter of shaft II are cut into the tube at a level below thewater level. Two inlet holes [6 are out just below and Six outlet holes8 for admitting atmospheric air is provided above the water level.

A glass receptacle I9 is detachably mounted by a supporting arm 20,pivoted about the sleeve i. The receptacle is centered about the tube l3by projections 2i extending radially outwardly from a ring 22frictionally attached to the tube,

- and by bearing against the bottom of the tube at-its conical bottom23. By swinging the arm slid downwardly. The receptacle' has anannularenlargement or shoulder 24 near the-top." The size of the receptacle issuch that the watersample (100 ml. in :the usual test) hasits level 25 afew millimeters above the floor-of the enlargement 24. Graduations, suchas 5,10, 15,25,450, 75 and 100 mlvmarks may be. engraved on-the glass.

A burette 26 or similar measuring and-dispensing device is mounted onsleeve 4 by-a clamp2l, and located toadmit the standard soap solutioninto the receptacle at arate regulated by 'the'cock 23. A rate of flowof 1 ml. per minuteis preferred, although rates as high as 3 or 4ml.--per minute of soap solution of the-'strengthdescribed heretoforefor the hand method ma'y be employed.

- An electric lamp is mountedin a metallic 'con-.

tainer 29 having a window- 30-at the 1evel of the observing holes 15;it-is-wired' so asto remain illuminated when the motoris stopped.

To run a test, the water is placed'in thereceptacle to the level 25 andthe motoris started,

causing a vortex to formin the -draft "tube I3, and causing airadmittedthroughhole Hi to all of the air bubbles tomove toward" thedrafttube and to enter the tube through the inlet holes it, together with aconsiderable amount of water, as indicated by the arrows. A. :Therecirculation of the-air through the holes I6 is preferred and canbeeffected by a proper proportioning of the diameters of the receptacleI9 and the tube i3,.one. example of correct dimensions being givenbelow. Devices of'different diameters wherein the air is notrecirculated through holes Hi can also be employed, but in such devicesthe air .flows past the .observing holes l5, thereby detracting from thesharpness of the end point.

The soap is. then admitted gradually ordropwise from the burette 26, theair-in-water dispersion being observed against the lightthrough theholes 55. (It is also possibleto observe .the air-.in-water dispersionagainst daylight.) The receptacle !9 at the level .of thevholesl5 thusforms an observing zone. At first and throughout most of the titration,the air bubbles remain almost constant in size and number. As theequivalence point is approached they rapidly become smaller and morenumerous and the:air-

in-water dispersion assumes a turbid or milky appearance. This milkyappearance then becomes more intense until it obscures the light to suchan extent that the holesl5 cannot be distinguished from the otherportions of the tube i3. The cock 28 is then closed and the quantity ofsoap is read. The lather factor is subtracted from this quantity todetermine the hardness. While it is preferred to add soap until theholes l5 are totally obscured, the end point can also be determined byadding soap until they are almost obscured, i. e., it is possible toselectany desired predetermined degree of opacity or transparency of theair-in-water dispersion-for theend point, the only requirement beingthat the soap solution be standardized and the. lather-factor determinedunder the .samez conditionsand with the same end point.

When the end point is reached, or even sooner, a few globules or patchesof lather will at times appear on the surface of the air-in-waterdispersion, but these are not uniform, have no appreciable height, andgive no indication of the end point, the bulk of the soap being retainedin the air-in-water dispersion. It was found that usually between 0.5 to1.5 ml. of soap (of a strength equivalent to 1.0 mg. of calciumcarbonate per ml. of soap) in excess of that required to obscure theholes I5 must be added to form an unbroken layer of lather on thesurface at the ordinary operating speeds, this excess being, however,not uniform and being frequently equal to from 50 to 100% of theequivalent amount of soap. When, after reaching the proper end point byobserving the holes, the addition of soap and the rotation of the motorare stopped, a layer of lather of several millimeters in height rapidlybuilds up at the surface and the dispersion clears, causing the water tolose its opacity. If desired, the water can be left quiescent to observethe permanence of the lather, the enlargement 24 providing a largesurface area so as to facilitate this observation. Another means ofchecking the correctness of the end point consists in observing theapproximate time which is required for the clearing up of theair-in-water dispersion after the motor is stopped. A false end point isindicated by a rapid clearing of the air-in-water dispersion, usually 2or 3 seconds, whereas if the true end point has been reached 15 to 20seconds will be required. These observations of the lather or the timerequired for clearing are not, however, essential with this method. Whenthe speed of the motor is increased more air bubbles are formed andcirculated. The speed must not be so great as to draw in so much air andto disperse it so finely that opaque bubbles are formed before themagnesium has reacted with the soap, as was explained heretofore; on theother hand, the minimum speed must be sufficient to induce a completeprecipitation of the insoluble soaps when the equivalent amount of soapis present. Operations between these limits of speed (which may, forexample, be between 3,000 and 8,000 revolutions per minute for thedevice shown) are possible. For precise determinations it is, however,desirable that the speed be always the same or about the same, i. e.,that it vary not more than about three or four hundred revolutions perminute, because variations in speed affect the appearance of theair-in-water dispersion and result in different end points. A tachometercan be used to indicate the speed.

The speed can be conveniently regulated without a tachometer as follows:When the rheostat S is adjusted to increase the speed a secondary vortexof air is formed in the conical bottom 23 beneath the draft tube I3,extending further down as the speed is increased until it reaches thebottom of the receptacle. When no vortex appears in the cone 23 it isnot known whether the speed is too low, and when it reaches the bottomof the receptacle it is not known whether the speed is too high. It ispreferred to operate at a speed at which the vortex just barely oralmost touches the lower tip of the cone 23, but any position, such ashalf way down, may be selected. a

Without limiting the invention to particular dimensions, the followingfigures are given to describe the device found to give the best results:The height of the water level was 10.7 cm. above the bottom of the cone23, and 2 mm. above the floor of enlargement 24, which had a diameter of6.7 'cm.; the cone 23 was 2.5 cm. high; the internal diameter of themain portion of the receptacle was 3.5 cm.; the diameter of the drafttube I3 was 1.9 cm. outside, and 1.65 cm. inside; the diameters of theholes I5 and I6 were 1.5 cm; the diameters of the six holes H at thebottom were 0.5 cm. With this device a speed of about 6,000 revolutionsper minute was found to give excellent results.

In the form according to Figure 4, the end point is determined by meansof a photo-electric cell. The metallic container 29' carries a lamp 3I,lens 32 and reflecting mirror 33, for directing a beam of light throughthe water in the receptacle I9 and the observing holes I5 in the drafttube I3, into a photo-electric cell mounted in a container 34 carrying alight shield 35. When the end point is reached the opacity of the waterdiminishes the intensity of the beam and causes the photo-electric cellto indicate the end point by means of a light or other suitable signalnot shown or measuring means electrically connected to the cell.

It should be noted that when the light cell is applied to the deviceshown in Figures 1 to 3 the shaft I I does not entirely obscure thelight beam because its diameter is less than that of the holes I5; thelight beam may, however, also pass along side of the tube I3.

This embodiment is useful not only with the batch method describedaccording to Figures 1 to 3, but also in continuous methods wherein thesoap and water are continuously mixed with air and passed once onlythrough an observation Zone in a state of turbulence necessary toproduce the opacity, as described heretofore. Further, the continuousmethod can be combined with recirculation of water by continuouslyfeeding the soap and water into a receptacle such as that shown inFigures 1 to 3 and providing overflow means for withdrawing the water.In either the batch method or the continuous method the ratio of soap towater can be varied until the end point is reached, or a constantproportioned mixture of soap and water can be subjected to the test todetermine whether or not it contains the equivalent amount of soap.Visual observation is possible, but the photo-electric cell offerscertain advantages in industrial installations. Thus, in continuousmethods wherein a constant proportioned mixture is tested, the cell canbe wired to a signal, or to a recording device on a time chart, or to arelay-controlled valve to control the operation of a water softeningplant. When the ratio of soap to water is varied, the cell can also beconnected to record the hardness by recording the quantity of soaprequired to reach the end point; in batch methods this may be effectedby recording directly the quantity of soap required or the time requiredwhen soap is fed at a constant rate, to reach the end point, while incontinuous methods it can record the rate of flow of soap required toreach the end point when water is fed at a constant rate.

In practicing the method it is desirable to add about 1 ml. of asaturated aqueous solution of borax to the ml. water sample to controlthe pH, which is preferably about 9.2, to improve the accuracy bykeeping the amount of soap consumed by hydrolysis at a constant value.

When working with waters having a total hardness in excess of about 75parts per million of calcium carbonate, it is desirable to dilute thewater with an aliquot part of distilled water, and then test 100 ml. ofthe diluted water- The procedure may be reversed by gradually adding thewater instead of the soap. In this method about 50 to 75 ml. of thewater and sufficient soap'to render an air-in-water dispersioncontaining 80 to 100 ml. of the water opaque are placed in thereceptacle l9, and the motor is started. The balance of the water isplaced in the burette, and added gradually, until it is just possible todistinguish the observing holes l from the tube 13. When thispredetermined degree of opacity is reached the cock 28 is closed and thetotal quantity of water is determined.

The methods described heretofore yield the total hardness. The hardnessdue to each of the several metals can also be determined byprecipitating one or more of them and running a test on such metal ormetals as remain in solution. Thus, when water contains only calcium andmagnesium, a 100 ml. sample may be treated with 2 ml. of saturatedaqueous sodium oxalate, left to stand for minutes to 2 hours, andsubjected to the test, (either together with the precipitate or afterfiltering) to find the hardness due to magnesium. Similarly, themagnesium may be removed from the reaction by treating another samplewith an acid to convert the carbonate ions to carbonic acid;subsequently removing the latter by aeration, and finally adding sodiumhydroxide. The resulting alkaline water can then be tested for calciumhardness. The aeration which causes the vaporization of carbonic acidcan be carried out in the apparatus illustrated by v operating the motorwhich disperses air in the acidified water to aerate the same.

I claim as my invention:

1. A method for determining the equivalent amounts of soap and watercomprising the steps of commingling measured amounts of soap and Water,dispersing air in the resulting soap and water mixture, continuouslycirculating the resulting air-in-water dispersion through a confinedspace provided with an optical path beneath the surface of thedispersion while maintaining the dispersion in a state of turbulencesufficient to prevent the formation of a substantial layer of lather onthe surface of the dispersion and to retain substantially all of thesoap beneath the surface when the quantity of soap in the dispersion issufficient to form a lather on the surface in the quiescent state, andmeasuring the relative opacity of the dispersion fiowing through saidconfined space.

2. A method for determining the equivalent amounts of soap and watercomprising the steps of commingling measured amounts of soap and water,dispersing air in the resulting soap and water mixture, continuouslycirculating the resulting air-in-water dispersion through a confinedspace provided with an optical path beneath the surface of thedispersion while maintaining the dispersion in a state of turbulencesufiicient to prevent the formation of a substantial layer of lather onthe surface of the dispersion and to retain substantially all of thesoap beneath the surface when the quantity of soap in the dispersion issufficient to form a lather on the surface in the quiescent state, andprogressively adding measured increments of soap until the dispersionflowing through said confined space becomes opaque.

3. A method for determining the equivalent amounts of soap and watercomprising the steps of commingling measured amounts of soap and water,imparting a rotary motion to the resulting soap and water mixture in aconfined zone sufficient to form a vortex and to disperse air in themixture, continuously flowing the resulting airin-water dispersionthrough a confined space provided with an optical path beneath thesurface of the dispersion whilemaintaining the dispersion in a state ofturbulence sufficient to prevent the formation of a substantial layer oflather on the surface of the dispersion and to retain substantially allof the soap beneath the surface when the quantity of soap in thedispersion is suficient to form a lather on the surface in the quiescentstate, and measuring the relative opacity of the dispersion flowingthrough said confined space.

4. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold water, a draft tube in saidreceptacle, inlet and outlet means for said draft tube in communicationwith the water at different points in the draft tube, propeller meanswithin the draft arranged to circulate water through said draft tube andthrough said inlet and outlet means, and means for dispersing air in thewater to produce an air-in-water dispersion which becomes opaque in thepresence of soap.

5. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold Water, a draft tube in saidreceptacle, inlet and outlet means for said draft tube in communicationwith the water at different points in the draft tube, propeller meanswithin the draft tube arranged to circulate water through.

said draft tube and through said inlet and outlet means, means fordispersing air in the water to produce an air-in-water dispersion,asource of light disposed to direct a beam of light through the body ofdispersion in the receptacle, and a light sensitive cell in the path ofsaid beam, the cell, source of light, and receptacle being so arrangedthat when the dispersion becomes opaque the light beam is difiused andlessened in intensity before it reaches the cell.

6. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold soap and water, means fordispersing air in the water and soap mixture, and for mixing the airwith the Water and soap mixture with a turbulence such as to form anair-inwater dispersion which dispersion is rendered. substantiallyopaque when an equivalent amount of soap is inthe water, a source oflight disposed to direct a beam of light through the body of theturbulent dispersion in the receptacle, and a light sensitive cell inthe path of said beam, the cell, the source of light, and the receptaclebeing so disposed that when the turbulent dispersion becomes opaque thelight beam is diffused and lessened in intensity before it reaches thecell.

7. An apparatus for testing water with respect to' soap comprising atransparent receptacle adapted to hold water, a vertical draft tube insaid receptacle, inlet means for said draft tube located to admit waterand air into the tube at a point spaced substantially from the bottom incommunication with the Water, means for admitting air into the drafttube, a part of the draft tube being cut away at a level above saidinlet means and below the surface of the water to provide an opticalpath, outlet means for said draft tube located near the bottom of thetube to dis charge water and air into the receptacle, and propellermeans within the draft tube arranged to impart a downward rotationalmovement to water within the draft tube with a velocity sufficient todisperse air in the water.

8. The apparatus according to claim '7 wherein the apparatus comprises asource of light disposed to direct a beam of light through said opticalpath and a light sensitive cell in the path of the beamof light after itemerges from said optical path..

9. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold water, having a generallycylindrical lower body portion on the lower portion of which is ofgradually diminishing cross sectional area, a vertical draft tube openat the bottom extending to said bottom so as to provide a space beneathsaiddraft tube wherein an air vortex can be formed, inlet means for saiddraft tube located to admit water and air into the tube at a pointspaced substantially from the bottom in communication with the water,means for admitting air into the draft tube, outlet means in the side ofsaid draft tube near the bottom of the tube to discharge water and airinto the receptacle near the bottom, and propeller means within thedraft tube arranged to impart downward and rotational movement to waterwithin the draft tube with a velocity sufficient to disperse air in thewater and toform a secondary air vertex in the space beneath the drafttube.

10. An apparatus for determining the equivalent amounts of soap andwater, comprising a transparent receptacle adapted to hold water havinga generally cylindrical lower body portion and an annular enlargementabove said body portion, a vertical draft tube in said receptacle, inletmeans for said draft tube located to admit water and air into said tubeat a point spaced substantially from the bottom in communication withthe water, means for admitting atmospheric air into the draft tube,outlet means for said draft tube located near the bottom of the tube todischarge water and air into the receptacle, propeller means within thedraft tube arranged to impart a downward and rotational movement towater within the draft tube with a velocity suflicient to disperse airin the water, and means for introducing measured quantities of liquidinto said receptacle.

11. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold water, a vertical draft tube insaid receptacle, inlet means for said draft tube located to admit waterand air into said tube at a point spaced substantially from the bottom,in communication with the water, means for admitting atmospheric airinto the draft tube, outlet means for said draft tube located near thebottom of the tube to discharge water and air into the receptacle, andpropeller means within the draft tube arranged to impart a downward androtational movement to water within the draft tube with a velocitysufiicient to disperse air inthe water, the relative sizes of thereceptacle and draft tube being such that a major portion of the airdischarged through said outletmeans is caused to be displaced radiallyinwardly in the receptacle and to enter the draft tube through saidinlet means together with water.

12. An apparatus for testing water with respect to soap, comprising atransparent receptacle adapted to hold water, a vertical draft tube insaid receptacle, inlet means for said draft tube located to admit waterand air into the draft tube at a level above the bottom and below thesurface of the water, means for admitting air into the draft tube,outlet means below said inlet means to discharge water and air into thereceptacle, propeller means within the draft tube arranged to impart adownward and rotational movement to water within the draft tube with avelocity to disperse air in the water, and a lamp arranged to directlight through the receptacle.

13. The apparatus according to claim 12 wherein the lamp is located todirect a beam of light through the receptacle at a level above the levelof said inlet means and below the surface of the water, and a part ofthe draft tube is cut away at the level of the lamp so as to permit abeam of light to pass from the lamp through the receptacle and throughthe draft tube.

WILFRED F. LANGELIER.

